The present invention is directed to anisotropic heat-curable monomers and to thermoset resins prepared therefrom.
Multi-functional heat-curable monomers are known which can be employed in the production of thermosetting composites such as, for example, epoxy-based compositions. However, one disadvantage with such known thermosetting compositions is that they tend to shrink to an undesirable degree subsequent to the crosslinking reaction.
It is also known to produce anisotropic, heat-curable acrylic-terminated monomers. U.S. Pat. No. 4,452,993 to Conciatori et al (assigned to the assignee of the present invention) discloses such monomers having the formula: ##STR1## wherein Ar is a divalent radical comprising at least one aromatic ring, Ar.sub.1 is a divalent radical selected from the group consisting of phenylene, naphthalene, biphenylene and mixtures thereof and R is selected from the group consisting of hydrogen and methyl. Although the monomers of Conciatori et al possess the desirable characteristics of having self-reinforcing properties due to their ability to form a molecularly oriented anisotropic melt and of being crosslinkable due to their unsaturated end groups, due to the highly aromatic nature of the monomer (i.e., the monomer being devoid of aliphatic units in the main chain) the monomer is extremely rigid and quickly becomes brittle upon crosslinking. Further, the rigidity of the monomer may limit crosslinking of the same.
U.S. Pat. No. 3,770,811 to Lee et al discloses acrylic terminated compounds of the formula: ##STR2## wherein R is selected from ##STR3## and R.sub.1 is hydrogen, lower alkyl, or halogen, which compounds are said to be useful as binders in dental restorative compositions. However, these monomers, which contain one to two aromatic rings, are not capable of forming anisotropic melts and thus are not suitable for uses requiring a molecularly ordered polymer.
U.S. Pat. No. 3,066,112 to Bowen discloses a compound of the formula ##STR4## However, inasmuch as this compound has only two aromatic rings, it is likely to have the same defects as above.
Also, U.S. Pat. No. 3,657,384 to Yoshida et al discloses a thermoplastic copolymer prepared by copolymerizing at least one monoethylenically unsaturated carboxylic acid and an aminoplast with a monomer having the general formula ##STR5## where n is an integer from zero to five. However, it is unlikely that either of the foregoing monomers form liquid crystalline melts due to the relatively high ratio of aliphatic to aromatic groups.
U.S. Pat. No. 2,928,804 to Foster et al discloses polymerizable esters of the general formula ##STR6## where n is an integer from zero to five. However, it is unlikely that either of the foregoing monomers form liquid crystalline melts due to the relatively high ratio of aliphatic to aromatic groups.
U.S. Pat. No. 4,068,082 to Stoffey et al discloses an ester of the following formula ##STR7## wherein R.sub.1, R.sub.2 and R.sub.3 are either hydrogen or lower alkyl groups preferably comprising four or less carbon atoms. However, the same defects as above are likely to be present due to the low aromaticity of the monomer.
U.S. Pat. No. 4,144,283 to Matsubara discloses a curable coating composition of the formula: ##STR8## wherein X is selected from the group consisting of methyl and methoxy groups and a chlorine atom, R.sub.1 and R.sub.2 are each a hydrogen atom or methyl group, m is zero or one, y is an integer of two to four, and n is an integer of 1 to 10. However, these monomers do not form anisotropic melts.